Toxic is a good choice for Altaria as it has excellent defense. Dragon Pulse is a MUST for STAB. Flamethrower is excellent too. As DT said, dragon dance is useless. Air cutter is good if he has higher special attack. Fly is waay to predictable.

You should go with toxic for sure. You obviously need dragon pulse. Roost might be good, but I don't like losing flying type. Safegaurd is good if you are fast, if not refresh is better. Air cutter would be great and flamethrower is a must have.

A special set is also a possibility as Altaria has Draco Meteor, Flamethrower, and HP Ground. It also has some use as a tricky Sleep counter by just running Sleep Talk, making any phazing attempts useless.

This thing is deadly after it sets up a Dragon Dance, which it can easily do with great defenses and typing that gives a lot of resistances with the handy Dragon immunity. Not too many things out there can take a +1 Pixilated Return or Frustration, much less at +2. Roost is to heal off damage with your surprisingly good bulk despite being uninvested. Earthquake is excellent coverage that hits what Return can't (especially Heatran), but Heal Bell or Subsitute can be used if you hate status.

248 HP EVs allow Altaria to switch into Stealth Rock 4 times without fainting, but it also helps a little even if it only does it once. A spinner is recommended though.
Physical bulk is invested in so Altaria has best overall bulk since it's SpD is higher than Def.
Dragon Dance is used to boost Speed and Attack, making it more powerful, and faster. Easily gets away with it having Roost as reliable recovery.
Dragon Claw is STAB and has good neutral coverage, Earthquake complements it nicely by hitting Steel types that resists Dragon Claw.

The bulkiest Dragon in NU is a beast with the right set. And his cursed 4x weakness to Ice is hard on him, but he can usually take it like a baws.

Altaria @ Leftovers
Natural Cure
Calm
252 HP/ 4 Def/ 252 SpD

Cotton Guard
Roost
Dragon Pulse
Toxic

One Cotton Guard can make this guy a beast. Adn two makes him BAWS. Roost removes that 4x weakness and heals him. Dragon Pulse prevents him from becoming Taunt bait. Toxic is also useful to force switches because of the quicklt dwindling HP.

Altaria@Leppa Berry. Natural Cure
Cotton Guard: Raise Altaria's already great defense
Draco Meteor: 210 damage including stab. Lowers Sp. Attack, which is good for next attack
Power Swap: That -2 special attack? Give it to the opponent
Roost: For hp

Altaria (F) @ Metal Coat

Steel Wing: Covers 3/4 weaknesses (Rock, Ice, and Fairy).Dragon Dance: Power up!Cotton Guard: Use twice, and poof. Cotton goes poof, and your defense is now as high as @$&!Dragon Claw: Sure it covers Dragon weakness, but... How does this thing even learn Dragon Claw??!

Stalling Moveset

Altaria (F) @ Leftovers

Trait: Cloud Nine
Nature: Jolly
EVs: 252 HP / 126 SpDef / 126 Def

Cotton Guard: Raise your def and take them hits!Roost: Heal up after waiting for... Toxic: Everyone's favorite stalling move, except when it's used against them. Steel Wing: If you're just waiting for toxic to finish the job, throw in a steel wing or two. Also here to cover weaknesses (Ice, Rock, and Fairy... Which is a nice 3/4 weaknesses covered with one move.).